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COBOL Tutorial

COBOL PROPERTY - Object-Oriented Properties

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What is PROPERTY?

PROPERTY in COBOL is a fundamental concept in object-oriented programming that provides controlled access to data fields within a class. Think of it as a smart container that not only holds data but also controls how that data can be accessed and modified - it's like having a security guard that checks credentials before allowing access to valuable information.

🏠 Real-World Analogy

Imagine a smart home security system:

  • PROPERTY: Like a secure room with controlled access
  • GET Method: Like checking what's in the room (read access)
  • SET Method: Like putting something in the room (write access)
  • Validation: Like security checks before allowing entry
  • Encapsulation: Like keeping the room's contents private

PROPERTY in COBOL works the same way - it protects and controls access to your data.

Key Features

  • Data Encapsulation - Protects data from direct access
  • Controlled Access - GET and SET methods for data access
  • Validation Support - Can validate data before assignment
  • Business Logic - Can include business rules in access methods
  • Inheritance Support - Can be inherited and overridden
  • Type Safety - Ensures data type consistency
  • Error Handling - Can handle invalid data gracefully
  • Documentation - Self-documenting interface

How to Use PROPERTY

Using PROPERTY in COBOL involves defining the property data field and implementing GET and SET methods to control access to that data.

Basic PROPERTY Implementation

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* Basic PROPERTY implementation
       CLASS-ID. CUSTOMER-CLASS.
       
       ENVIRONMENT DIVISION.
       CONFIGURATION SECTION.
       
       DATA DIVISION.
       WORKING-STORAGE SECTION.
       01  CUSTOMER-NAME    PIC X(30).
       01  CUSTOMER-AGE     PIC 9(3).
       01  CUSTOMER-EMAIL   PIC X(50).
       
       OBJECT SECTION.
       CLASS CUSTOMER-CLASS.
       
           * Property definitions
           PROPERTY NAME IS CUSTOMER-NAME
           PROPERTY AGE IS CUSTOMER-AGE
           PROPERTY EMAIL IS CUSTOMER-EMAIL
       
           * GET method for NAME property
           METHOD-ID. GET-NAME.
           DATA DIVISION.
           LINKAGE SECTION.
           01  RETURN-NAME   PIC X(30).
           PROCEDURE DIVISION RETURNING RETURN-NAME.
               MOVE CUSTOMER-NAME TO RETURN-NAME
               EXIT METHOD.
           END METHOD GET-NAME.
       
           * SET method for NAME property
           METHOD-ID. SET-NAME.
           DATA DIVISION.
           LINKAGE SECTION.
           01  NEW-NAME      PIC X(30).
           PROCEDURE DIVISION USING NEW-NAME.
               * Validation logic
               IF NEW-NAME = SPACES
                   DISPLAY "Error: Name cannot be empty"
               ELSE
                   MOVE NEW-NAME TO CUSTOMER-NAME
               END-IF
               EXIT METHOD.
           END METHOD SET-NAME.
       
           * GET method for AGE property
           METHOD-ID. GET-AGE.
           DATA DIVISION.
           LINKAGE SECTION.
           01  RETURN-AGE    PIC 9(3).
           PROCEDURE DIVISION RETURNING RETURN-AGE.
               MOVE CUSTOMER-AGE TO RETURN-AGE
               EXIT METHOD.
           END METHOD GET-AGE.
       
           * SET method for AGE property with validation
           METHOD-ID. SET-AGE.
           DATA DIVISION.
           LINKAGE SECTION.
           01  NEW-AGE       PIC 9(3).
           PROCEDURE DIVISION USING NEW-AGE.
               * Age validation
               IF NEW-AGE < 0 OR NEW-AGE > 150
                   DISPLAY "Error: Invalid age value"
               ELSE
                   MOVE NEW-AGE TO CUSTOMER-AGE
               END-IF
               EXIT METHOD.
           END METHOD SET-AGE.
       
       END CLASS CUSTOMER-CLASS.

This example shows basic property implementation with GET and SET methods including validation.

PROPERTY Operations

OperationSyntaxExample
Define propertyPROPERTY name IS data-fieldPROPERTY NAME IS CUSTOMER-NAME
GET methodMETHOD-ID. GET-name. RETURNING return-fieldMETHOD-ID. GET-NAME. RETURNING RETURN-NAME
SET methodMETHOD-ID. SET-name. USING input-fieldMETHOD-ID. SET-NAME. USING NEW-NAME
Access propertyINVOKE object "GET-name" RETURNING valueINVOKE CUSTOMER "GET-NAME" RETURNING NAME
Set propertyINVOKE object "SET-name" USING valueINVOKE CUSTOMER "SET-NAME" USING NEW-NAME

Practical Examples

Let's look at some real-world examples of how PROPERTY is used in COBOL applications.

Bank Account with Properties

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* Bank account class with properties
       CLASS-ID. BANK-ACCOUNT.
       
       DATA DIVISION.
       WORKING-STORAGE SECTION.
       01  ACCOUNT-NUMBER   PIC 9(10).
       01  ACCOUNT-BALANCE  PIC 9(8)V99.
       01  ACCOUNT-HOLDER   PIC X(30).
       01  ACCOUNT-TYPE     PIC X(10).
       01  MIN-BALANCE      PIC 9(8)V99 VALUE 100.00.
       
       OBJECT SECTION.
       CLASS BANK-ACCOUNT.
       
           * Property definitions
           PROPERTY ACCOUNT-NUMBER IS ACCOUNT-NUMBER
           PROPERTY BALANCE IS ACCOUNT-BALANCE
           PROPERTY HOLDER IS ACCOUNT-HOLDER
           PROPERTY TYPE IS ACCOUNT-TYPE
       
           * GET method for ACCOUNT-NUMBER (read-only)
           METHOD-ID. GET-ACCOUNT-NUMBER.
           DATA DIVISION.
           LINKAGE SECTION.
           01  RETURN-NUMBER PIC 9(10).
           PROCEDURE DIVISION RETURNING RETURN-NUMBER.
               MOVE ACCOUNT-NUMBER TO RETURN-NUMBER
               EXIT METHOD.
           END METHOD GET-ACCOUNT-NUMBER.
       
           * SET method for ACCOUNT-NUMBER with validation
           METHOD-ID. SET-ACCOUNT-NUMBER.
           DATA DIVISION.
           LINKAGE SECTION.
           01  NEW-NUMBER    PIC 9(10).
           PROCEDURE DIVISION USING NEW-NUMBER.
               * Account number validation
               IF NEW-NUMBER = 0
                   DISPLAY "Error: Invalid account number"
               ELSE
                   MOVE NEW-NUMBER TO ACCOUNT-NUMBER
               END-IF
               EXIT METHOD.
           END METHOD SET-ACCOUNT-NUMBER.
       
           * GET method for BALANCE
           METHOD-ID. GET-BALANCE.
           DATA DIVISION.
           LINKAGE SECTION.
           01  RETURN-BALANCE PIC 9(8)V99.
           PROCEDURE DIVISION RETURNING RETURN-BALANCE.
               MOVE ACCOUNT-BALANCE TO RETURN-BALANCE
               EXIT METHOD.
           END METHOD GET-BALANCE.
       
           * SET method for BALANCE with business rules
           METHOD-ID. SET-BALANCE.
           DATA DIVISION.
           LINKAGE SECTION.
           01  NEW-BALANCE   PIC 9(8)V99.
           PROCEDURE DIVISION USING NEW-BALANCE.
               * Balance validation
               IF NEW-BALANCE < 0
                   DISPLAY "Error: Balance cannot be negative"
               ELSE IF NEW-BALANCE < MIN-BALANCE
                   DISPLAY "Warning: Balance below minimum"
                   MOVE NEW-BALANCE TO ACCOUNT-BALANCE
               ELSE
                   MOVE NEW-BALANCE TO ACCOUNT-BALANCE
               END-IF
               EXIT METHOD.
           END METHOD SET-BALANCE.
       
           * Deposit method using property
           METHOD-ID. DEPOSIT.
           DATA DIVISION.
           LINKAGE SECTION.
           01  DEPOSIT-AMOUNT PIC 9(8)V99.
           PROCEDURE DIVISION USING DEPOSIT-AMOUNT.
               * Validate deposit amount
               IF DEPOSIT-AMOUNT <= 0
                   DISPLAY "Error: Invalid deposit amount"
               ELSE
                   COMPUTE ACCOUNT-BALANCE = ACCOUNT-BALANCE + DEPOSIT-AMOUNT
                   DISPLAY "Deposit successful. New balance: " ACCOUNT-BALANCE
               END-IF
               EXIT METHOD.
           END METHOD DEPOSIT.
       
           * Withdraw method using property
           METHOD-ID. WITHDRAW.
           DATA DIVISION.
           LINKAGE SECTION.
           01  WITHDRAW-AMOUNT PIC 9(8)V99.
           01  SUCCESS-FLAG   PIC X(1).
           PROCEDURE DIVISION USING WITHDRAW-AMOUNT RETURNING SUCCESS-FLAG.
               * Validate withdrawal
               IF WITHDRAW-AMOUNT <= 0
                   MOVE "N" TO SUCCESS-FLAG
                   DISPLAY "Error: Invalid withdrawal amount"
               ELSE IF WITHDRAW-AMOUNT > ACCOUNT-BALANCE
                   MOVE "N" TO SUCCESS-FLAG
                   DISPLAY "Error: Insufficient funds"
               ELSE
                   COMPUTE ACCOUNT-BALANCE = ACCOUNT-BALANCE - WITHDRAW-AMOUNT
                   MOVE "Y" TO SUCCESS-FLAG
                   DISPLAY "Withdrawal successful. New balance: " ACCOUNT-BALANCE
               END-IF
               EXIT METHOD.
           END METHOD WITHDRAW.
       
       END CLASS BANK-ACCOUNT.

This example shows a bank account class with properties for account data and business logic.

Employee Management System

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* Employee class with computed properties
       CLASS-ID. EMPLOYEE.
       
       DATA DIVISION.
       WORKING-STORAGE SECTION.
       01  EMPLOYEE-ID      PIC 9(6).
       01  EMPLOYEE-NAME    PIC X(30).
       01  EMPLOYEE-SALARY  PIC 9(8)V99.
       01  EMPLOYEE-YEARS   PIC 9(2).
       01  BONUS-RATE       PIC 9V99 VALUE 0.10.
       
       OBJECT SECTION.
       CLASS EMPLOYEE.
       
           * Property definitions
           PROPERTY ID IS EMPLOYEE-ID
           PROPERTY NAME IS EMPLOYEE-NAME
           PROPERTY SALARY IS EMPLOYEE-SALARY
           PROPERTY YEARS IS EMPLOYEE-YEARS
       
           * GET method for computed bonus property
           METHOD-ID. GET-BONUS.
           DATA DIVISION.
           LINKAGE SECTION.
           01  RETURN-BONUS  PIC 9(8)V99.
           PROCEDURE DIVISION RETURNING RETURN-BONUS.
               * Calculate bonus based on salary and years
               COMPUTE RETURN-BONUS = EMPLOYEE-SALARY * BONUS-RATE * EMPLOYEE-YEARS
               EXIT METHOD.
           END METHOD GET-BONUS.
       
           * SET method for SALARY with validation
           METHOD-ID. SET-SALARY.
           DATA DIVISION.
           LINKAGE SECTION.
           01  NEW-SALARY    PIC 9(8)V99.
           PROCEDURE DIVISION USING NEW-SALARY.
               * Salary validation
               IF NEW-SALARY < 0
                   DISPLAY "Error: Salary cannot be negative"
               ELSE IF NEW-SALARY < 20000
                   DISPLAY "Warning: Salary below minimum wage"
                   MOVE NEW-SALARY TO EMPLOYEE-SALARY
               ELSE
                   MOVE NEW-SALARY TO EMPLOYEE-SALARY
               END-IF
               EXIT METHOD.
           END METHOD SET-SALARY.
       
           * GET method for YEARS with computed seniority
           METHOD-ID. GET-SENIORITY.
           DATA DIVISION.
           LINKAGE SECTION.
           01  SENIORITY-LEVEL PIC X(10).
           PROCEDURE DIVISION RETURNING SENIORITY-LEVEL.
               * Determine seniority level
               EVALUATE EMPLOYEE-YEARS
                   WHEN 0 THRU 2
                       MOVE "Junior" TO SENIORITY-LEVEL
                   WHEN 3 THRU 5
                       MOVE "Mid-Level" TO SENIORITY-LEVEL
                   WHEN 6 THRU 10
                       MOVE "Senior" TO SENIORITY-LEVEL
                   WHEN OTHER
                       MOVE "Expert" TO SENIORITY-LEVEL
               END-EVALUATE
               EXIT METHOD.
           END METHOD GET-SENIORITY.
       
           * Method to display employee information
           METHOD-ID. DISPLAY-INFO.
           DATA DIVISION.
           LINKAGE SECTION.
           01  BONUS-AMOUNT  PIC 9(8)V99.
           01  SENIORITY     PIC X(10).
           PROCEDURE DIVISION.
               * Get computed properties
               INVOKE SELF "GET-BONUS" RETURNING BONUS-AMOUNT
               INVOKE SELF "GET-SENIORITY" RETURNING SENIORITY
               
               * Display employee information
               DISPLAY "Employee ID: " EMPLOYEE-ID
               DISPLAY "Name: " EMPLOYEE-NAME
               DISPLAY "Salary: " EMPLOYEE-SALARY
               DISPLAY "Years: " EMPLOYEE-YEARS
               DISPLAY "Seniority: " SENIORITY
               DISPLAY "Bonus: " BONUS-AMOUNT
               EXIT METHOD.
           END METHOD DISPLAY-INFO.
       
       END CLASS EMPLOYEE.

This example demonstrates computed properties and business logic in an employee management system.

Advanced PROPERTY Features

PROPERTY supports advanced features for complex object-oriented programming scenarios.

Read-Only and Write-Only Properties

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* Properties with different access levels
       CLASS-ID. SECURE-DATA.
       
       DATA DIVISION.
       WORKING-STORAGE SECTION.
       01  SECRET-KEY       PIC X(20).
       01  ACCESS-COUNT     PIC 9(5) VALUE 0.
       01  LAST-ACCESS-DATE PIC 9(8).
       
       OBJECT SECTION.
       CLASS SECURE-DATA.
       
           * Read-only property (only GET method)
           PROPERTY ACCESS-COUNT IS ACCESS-COUNT
       
           * Write-only property (only SET method)
           PROPERTY SECRET-KEY IS SECRET-KEY
       
           * GET method for ACCESS-COUNT (read-only)
           METHOD-ID. GET-ACCESS-COUNT.
           DATA DIVISION.
           LINKAGE SECTION.
           01  RETURN-COUNT  PIC 9(5).
           PROCEDURE DIVISION RETURNING RETURN-COUNT.
               MOVE ACCESS-COUNT TO RETURN-COUNT
               EXIT METHOD.
           END METHOD GET-ACCESS-COUNT.
       
           * SET method for SECRET-KEY (write-only)
           METHOD-ID. SET-SECRET-KEY.
           DATA DIVISION.
           LINKAGE SECTION.
           01  NEW-KEY       PIC X(20).
           PROCEDURE DIVISION USING NEW-KEY.
               * Validation and logging
               IF NEW-KEY = SPACES
                   DISPLAY "Error: Secret key cannot be empty"
               ELSE
                   MOVE NEW-KEY TO SECRET-KEY
                   ADD 1 TO ACCESS-COUNT
                   MOVE FUNCTION CURRENT-DATE(1:8) TO LAST-ACCESS-DATE
                   DISPLAY "Secret key updated successfully"
               END-IF
               EXIT METHOD.
           END METHOD SET-SECRET-KEY.
       
           * Method to check if secret key is set
           METHOD-ID. HAS-SECRET-KEY.
           DATA DIVISION.
           LINKAGE SECTION.
           01  HAS-KEY       PIC X(1).
           PROCEDURE DIVISION RETURNING HAS-KEY.
               IF SECRET-KEY = SPACES
                   MOVE "N" TO HAS-KEY
               ELSE
                   MOVE "Y" TO HAS-KEY
               END-IF
               EXIT METHOD.
           END METHOD HAS-SECRET-KEY.
       
       END CLASS SECURE-DATA.

This example shows read-only and write-only properties with different access levels.

Property Inheritance and Overriding

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* Property inheritance example
       CLASS-ID. VEHICLE.
       
       DATA DIVISION.
       WORKING-STORAGE SECTION.
       01  VEHICLE-MAKE     PIC X(20).
       01  VEHICLE-MODEL    PIC X(20).
       01  VEHICLE-YEAR     PIC 9(4).
       
       OBJECT SECTION.
       CLASS VEHICLE.
       
           * Base properties
           PROPERTY MAKE IS VEHICLE-MAKE
           PROPERTY MODEL IS VEHICLE-MODEL
           PROPERTY YEAR IS VEHICLE-YEAR
       
           * GET method for MAKE
           METHOD-ID. GET-MAKE.
           DATA DIVISION.
           LINKAGE SECTION.
           01  RETURN-MAKE   PIC X(20).
           PROCEDURE DIVISION RETURNING RETURN-MAKE.
               MOVE VEHICLE-MAKE TO RETURN-MAKE
               EXIT METHOD.
           END METHOD GET-MAKE.
       
           * SET method for MAKE
           METHOD-ID. SET-MAKE.
           DATA DIVISION.
           LINKAGE SECTION.
           01  NEW-MAKE      PIC X(20).
           PROCEDURE DIVISION USING NEW-MAKE.
               MOVE NEW-MAKE TO VEHICLE-MAKE
               EXIT METHOD.
           END METHOD SET-MAKE.
       
       END CLASS VEHICLE.
       
       * Car class inheriting from Vehicle
       CLASS-ID. CAR INHERITS FROM VEHICLE.
       
       DATA DIVISION.
       WORKING-STORAGE SECTION.
       01  CAR-DOORS        PIC 9(1).
       01  CAR-COLOR        PIC X(15).
       
       OBJECT SECTION.
       CLASS CAR.
       
           * Additional properties for Car
           PROPERTY DOORS IS CAR-DOORS
           PROPERTY COLOR IS CAR-COLOR
       
           * Override SET method for MAKE with validation
           METHOD-ID. SET-MAKE OVERRIDE.
           DATA DIVISION.
           LINKAGE SECTION.
           01  NEW-MAKE      PIC X(20).
           PROCEDURE DIVISION USING NEW-MAKE.
               * Car-specific validation
               IF NEW-MAKE = "INVALID"
                   DISPLAY "Error: Invalid make for car"
               ELSE
                   * Call parent method
                   INVOKE SUPER "SET-MAKE" USING NEW-MAKE
               END-IF
               EXIT METHOD.
           END METHOD SET-MAKE.
       
           * SET method for DOORS with validation
           METHOD-ID. SET-DOORS.
           DATA DIVISION.
           LINKAGE SECTION.
           01  NEW-DOORS     PIC 9(1).
           PROCEDURE DIVISION USING NEW-DOORS.
               * Door validation
               IF NEW-DOORS < 2 OR NEW-DOORS > 5
                   DISPLAY "Error: Invalid number of doors"
               ELSE
                   MOVE NEW-DOORS TO CAR-DOORS
               END-IF
               EXIT METHOD.
           END METHOD SET-DOORS.
       
       END CLASS CAR.

This example demonstrates property inheritance and method overriding in COBOL.

Best Practices and Tips

Following these best practices will help you use PROPERTY effectively in your COBOL applications.

PROPERTY Best Practices

  • Always validate in SET methods - Ensure data integrity through validation
  • Use meaningful property names - Choose descriptive names for properties
  • Implement proper error handling - Handle validation failures gracefully
  • Document property behavior - Document expected values and constraints
  • Use computed properties wisely - For derived values that don't need storage
  • Maintain consistency - Use consistent naming and access patterns
  • Consider access levels - Use read-only, write-only, or read-write as appropriate
  • Test property behavior - Thoroughly test GET and SET methods

Common Mistakes to Avoid

MistakeProblemSolution
No validation in SET methodsInvalid data can be storedAlways implement validation logic
Exposing internal dataBreaks encapsulationUse properties for controlled access
Inconsistent namingConfusing and hard to maintainUse consistent naming conventions
No error handlingProgram crashes on invalid dataImplement proper error handling
Over-complex propertiesHard to understand and debugKeep properties simple and focused
Ignoring inheritanceMissed opportunities for reuseUse inheritance appropriately

PROPERTY Quick Reference

ActionSyntaxExample
Define propertyPROPERTY name IS data-fieldPROPERTY NAME IS CUSTOMER-NAME
GET methodMETHOD-ID. GET-name. RETURNING return-fieldMETHOD-ID. GET-NAME. RETURNING RETURN-NAME
SET methodMETHOD-ID. SET-name. USING input-fieldMETHOD-ID. SET-NAME. USING NEW-NAME
Access propertyINVOKE object "GET-name" RETURNING valueINVOKE CUSTOMER "GET-NAME" RETURNING NAME
Set propertyINVOKE object "SET-name" USING valueINVOKE CUSTOMER "SET-NAME" USING NEW-NAME
Override methodMETHOD-ID. method-name OVERRIDEMETHOD-ID. SET-NAME OVERRIDE

Test Your Knowledge

1. What is PROPERTY in COBOL?

  • A data field for storing values
  • A mechanism for encapsulating data with controlled access in object-oriented COBOL
  • A file organization method
  • A program structure element

2. In which COBOL division is PROPERTY typically defined?

  • IDENTIFICATION DIVISION
  • ENVIRONMENT DIVISION
  • DATA DIVISION
  • PROCEDURE DIVISION

3. How do you access a PROPERTY in COBOL?

  • Directly using the property name
  • Using GET and SET methods
  • Using MOVE statements
  • Using DISPLAY statements

4. What is the main benefit of using PROPERTY in COBOL?

  • Faster program execution
  • Data encapsulation and controlled access
  • Reduced memory usage
  • Simpler program structure

5. Which COBOL feature is commonly used with PROPERTY for validation?

  • VALIDATE statement
  • GET and SET methods
  • IF statements
  • All of the above

Frequently Asked Questions

Related Concepts

Object-Oriented COBOL

Understanding object-oriented programming in COBOL.

Data Encapsulation

Working with data encapsulation concepts.

Method Overriding

Understanding method overriding in COBOL.

Inheritance in COBOL

Working with inheritance in object-oriented COBOL.

Class Design

Best practices for designing COBOL classes.

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